Diffusion

Definition

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. This process continues until equilibrium is reached, and it does not require cellular energy (ATP).

5 Must Know Facts For Your Next Test

1. Diffusion is driven by the kinetic energy of molecules.
2. It occurs along a concentration gradient, moving from high to low concentration.
3. No external energy or ATP is required for diffusion to occur.
4. Diffusion can occur across cell membranes if the molecules are small and nonpolar, such as oxygen or carbon dioxide.
5. The rate of diffusion can be influenced by temperature, molecular size, and the steepness of the concentration gradient.

Review Questions

• What drives the process of diffusion?
• Does diffusion require cellular energy? Explain why or why not.
• How does molecular size affect the rate of diffusion?

Related terms

Osmosis: The passive transport of water molecules across a semipermeable membrane from an area of lower solute concentration to higher solute concentration.

Facilitated Diffusion: The process by which molecules pass across the plasma membrane through cell membrane channels with the help of carrier proteins.

Concentration Gradient: A difference in the concentration of a substance across a space, which governs the direction and rate at which substances will diffuse.